GEOLOGY OF THE NORTHERN ADIRONDACK REGION 391 



Lowville limestone was deposited in these waters. The move- 

 ment of the region was apparently pivotal, along a northwest 

 and southeast axis which crossed at the upper end of the Ohain- 

 plain valley, sinking on the one side being accompanied by rise 

 on the other. In that district this line formed the southern 

 shore line of the Chazy sea and also the northern shore line of 

 the Lowville sea. The thinness and the intermittent character 

 of the Lowville formation, along the present line of the Mohawk 

 valley, would indicate either that the Lowville shore line was 

 nor far away to the north, and that the subsidence was only 

 trifling, or else that, after the deposition of the material, an 

 uplift occurred and considerable wear took place. So far as the 

 slender evidence goes, the former would seem to have been the 

 case, since the unconformity at the base of The Lowville is much 

 more pronounced than that at its summit, in fact there is little 

 sign of wear at the latter horizon; while the not infrequent oc- 

 currence of alternating Lowville and Black River conditions 

 would seem to bind the two formations rather closely together. 

 It is therefore thought probable that the Lowville sea extended 

 but little north of the Mohawk line and hence encroached little 

 or* not at all on the Adirondack region from the south. 



On the west side of the region the formation has much in- 

 creased thickness and apparently for many miles rests directly 

 <>n the old. Precambric floor. Its thickness would argue that 

 it must formerly have extended in several miles over the western 

 Adirondack border, and farther than any of the preceding seas 

 had done. 



During LoAvville time therefore the bulk of the Adirondack 

 region was a land area, with wide extent to the north and east 

 beyond the present boundaries of the district, with its southern 

 shore line rudely corresponding to the present Precambric bor- 

 der on that side, and its western edge alone somewhat submerged. 



The Black River limestone follows the Lowville on the south 

 and west, with no sign of a structural break between the two. 

 In the Mohawk valley the formation is thin and sometimes absent. 

 In some cases its nonappearance is definitely due to the fact that 

 the Lowville deposits had not completely filled the slight depres- 

 sions in the Beekmantown floor on which they were laid down, 



